Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$227.31	12.565%	$255.8715	$255.87	$255.85	$255.90
Purchase #2	$210.91	10.578%	$233.2201	$233.22	$233.20	$233.20
Purchase #3	$242.70	7.566%	$261.0627	$261.06	$261.05	$261.10
Purchase #4	$118.72	4.270%	$123.7893	$123.79	$123.80	$123.80
Purchase #5	$199.95	13.382%	$226.7073	$226.71	$226.70	$226.70
Purchase #6	$151.69	10.309%	$167.3277	$167.33	$167.35	$167.30
Purchase #7	$106.55	6.376%	$113.3436	$113.34	$113.35	$113.30
7 purchase totals =	$1,257.83		$1,381.3222	$1,381.32	$1,381.30	$1,381.30